This invention relates to improvements in motion sensors of the type in which a body of electrically conductive fluid is inertially displaced along a confined path through a magnetic field to induce therein an electric current reflecting the motion of the sensor body.
Sensors of the foregoing type, referred to as magnetohydrodynamic sensors, are generally well known and are usually operative to measure angular acceleration. Use of this type of sensor with modification to sense and thereby measure angular velocity is also known as disclosed in U.S. Pat. Nos. 3,618,399 and 4,188,576 to Aske and Jacob, respectively. According to the Aske patent, the sensor is provided with a measurement axis along which an output is obtained as its angular relationship to a sensitive axis varies with time during acceleration of the sensor about such sensitive axis. A velocity or angular rate measurement is extracted as a desired component of the output signal at the measurement axis by signal demodulating means. According to the Jacobs patent, fluid is ejected from a rotating nozzle as a free flowing jet through a magnetic field to induce current in the jet from which the angular rate measurement is extracted through pick-ups rotating with the nozzle. The foregoing angular motion sensors thus require moving parts and signal extracting electronics which severly limit velocity sensitivity.
It is therefore an important object of the present invention to provide a relatively small size magnetohydrodynamic sensor having no moving parts with an acceptable sensitivity to changes in angular rate for a useful range of angular vibration frequencies.
Another object is to provide a self-generating sensor of the foregoing type from which a measurable angular motion signal is directly obtained without amplification.